1. Field of the Invention
The present invention relates to a radio apparatus using a plurality of antennas, and more particularly to a multi-antenna radio apparatus with a simplified circuit structure.
2. Description of the Related Art
An adaptive array antenna system has a plurality of antennas, and detects the incident direction of radio wave from the phases of the radio wave received by the plurality of antennas to transmit a radio wave beam to the detected direction. For this purpose, it is necessary to correctly detect the phase difference in the received radio wave between the plurality of antennas.
However, in order to detect the phase difference in the radio wave between the antennas, it is generally necessary to convert the frequency of a radio frequency signal supplied from the respective antennas into a frequency adaptive for digital processing. In this case, frequency-converting sections provided for the antennas are required to perform the frequency conversion. Therefore, the apparatus became large in scale.
Also, when there is a phase drift in a local oscillation signal of each frequency converting section in the frequency conversion, the phase relation in the respective antennas is lost. For this reason, it is needed to use a local oscillation signal which is common to the frequency converting sections. In this case, it could be considered that another panel exclusive for the local oscillation signal is provided. However, because the local oscillation signal is distributed to each antenna, the local oscillation signal of the high precision becomes necessary to compensate for the distribution loss. Therefore, the unnecessary radiation becomes easy to generate. Also, the number of physical wiring lines increases. Thus, the facilities becomes large.
In conjunction with the above description, a receiving system is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 3-282278). In this reference, outputs from antenna elements of antenna systems are supplied to frequency converters (30, 3E, 3N). An output of a local oscillator (4) is spread in spreading units (50, 5E, 5N) with different codes which are generated by code generators (60, 6E, 6N). The spread signals are supplied to the frequency converters (30, 3E, 3N). Outputs of the frequency converters (30, 3E, 3N) are synthesized by a synthesizer (7) and amplified by an amplifier (8). The amplified signal is inversely spread in inversely spreading units (90, 9E, 9N) with outputs from the code generators (60, 6E, 6N).
Also, a spectrum spreading receiving apparatus is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 4-37340). In this reference, the spectrum spreading receiving apparatus includes N A/D converters and an adaptive filter for inputting outputs of the A/D converters to remove unnecessary frequency components. The spectrum spreading receiving apparatus is further composed of a reference signal generator, a calculator for calculating a correlation value of an output of the adaptive filter and an output of the reference signal generator, and a synchronization establishing means for establishing synchronization with a reception signal. The spectrum spreading receiving apparatus is further composed of means for dividing a calculation interval for the calculator into sub-intervals, and adding means for adding the correlation value at every sub-interval.
Also, a receiving apparatus is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 8-331011). In this reference, a summation calculating circuit receives an output of a correlating unit in a spreading communication system mobile station. The summation calculating circuit has a power mode and a quasi-delay detecting mode. Ones higher than a threshold value, of summation values from a plurality of calculating means are selected from the maximum summation value for a predetermined number.
Also, a spectrum spreading transmitting apparatus is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 9-64784). In this reference, a transmission data is divided into a plurality of data portions to elongate a period between data portions. The data portions are spread using different spreading codes with a long period. After reception, data portions are reproduced and integrated into the transmission data.
Also, a spectrum spreading radio transmitting apparatus is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 9-74372). In this reference, in the spectrum spreading radio receiving apparatus, a variable gain amplifiers (102-i) adjust amplification of signals received by a plurality of reception branches (101-i). An adder (103) adds the signals outputted from the variable gain amplifiers (102-i) to supply to an inverse spreading unit. A directionality control section (104) controls the amplification of each variable gain amplifier such that influence of a delayed wave having a delay smaller than a chip time width of the spread signal is reduced. Addition of the structure for an adaptive antenna system to control the directionality of the reception antennas to the spectrum spreading radio receiving apparatus with a RAKE receiving function make it possible to reduce the influences of an identical channel interference wave which cannot be measured by the RAKE receiving function and a delayed wave with a delay smaller than the chip time width of the spread signal.
Therefore, an object of the present invention is to provide a radio apparatus which can be simplified in the structure by use of spreading codes and inverse spreading codes.
Another object of the present invention is to provide a radio apparatus which can detect the incident direction of a radio wave with a simple structure so as to control the directionality of antennas.
Still another object of the present invention is to provide a radio apparatus which can reproduce a spread signal with a simple structure by use of spreading codes and inverse spreading codes while a plurality of antennas are used.
In order to achieve an aspect of the present invention, a radio apparatus includes a plurality of antennas, a plurality of spreading sections, a synthesizing section a converting section, a plurality of inverse spreading sections and a control unit. The plurality of antennas are provided at different physical positions to receive a radio wave signal, respectively. The plurality of spreading sections are provided for the plurality of antennas to spread the radio wave signal received by the plurality of antennas with spreading codes provided for the plurality of antennas to produce spread signals, respectively. The synthesizing section synthesizes the spread signals into an analog synthetic signal. The converting section converts the analog synthetic signal into a digital signal with a frequency such that a digital process can be applied to the digital signal. The plurality of inverse spreading sections are provided for the plurality of antennas to inversely spread the digital signal with inverse spreading codes provided for the plurality of antennas to produce inversely spread signals. The control unit controls orientation of the plurality of antennas based on the inversely spread signals.
The radio apparatus may further include a code generating section generating the spreading codes and the inverse spreading codes.
One of the spreading codes and a corresponding one of the inverse spreading codes have the same pattern and same phase. In this case, the spreading codes are peculiar to the plurality of antennas.
The radio wave signal may be of a TDMA system using a specific spreading code and a specific inverse spreading code. In this case, the spreading codes and the inverse spreading codes may be synchronous with the specific spreading code and the specific inverse spreading code, and have correlation with the specific spreading code and the specific inverse spreading code such that no influence is given to the specific spreading code and the specific inverse spreading code. Instead, the spreading codes and the inverse spreading codes may have a spreading gain such that no influence is given to the specific spreading code and the specific inverse spreading code.
The plurality of antennas preferably receive the radio wave signal to have phase shifts determined based on the physical positions.
In order to achieve another aspect of the present invention, a method of reproducing a digital signal in a radio apparatus, includes:
receiving a carrier signal by a plurality of antennas provided at different physical positions;
spreading the received carrier signals with spreading codes provided for the plurality of antennas;
synthesizing the spread signals into an analog synthetic signal;
converting the analog synthetic signal into a converted signal with a frequency such that a digital process can be applied to the digital signal; and
inversely spreading the converted signal with inverse spreading codes provided for the plurality of antennas so that digital signals can be reproduced.
In order to achieve still another aspect of the present invention, a radio apparatus includes a plurality of antennas, a plurality of spreading sections, a synthesizing section, a converting section, a plurality of first inverse spreading sections, and a plurality of second inverse spreading sections. The plurality of antennas are provided at different physical positions to receive a first multiplexed signal, respectively. The plurality of spreading sections are provided for said plurality of antennas to spread said first multiplexed signal received by said plurality of antennas with spreading codes provided for said plurality of antennas to produce spread signals, respectively. The synthesizing section synthesizes said spread signals into an analog synthetic signal. The converting section converting said analog synthetic signal into a digital signal with a frequency such that a digital process can be applied to said digital signal. The plurality of first inverse spreading sections are provided for said plurality of antennas, to inversely spread said digital signal with first inverse spreading codes provided for said plurality of antennas to produce second multiplexed signals. The plurality of second inverse spreading sections provided for said plurality of antennas, to inversely spread said second multiplexed signals with second inverse spreading codes provided for said plurality of antennas to reproduce channel signals.
The first spreading codes and the first inverse spreading codes have the same pattern and same phase.
The first spreading code and the first inverse spreading code may be synchronous with the second spreading code and the second inverse spreading code, and may have correlation with the second spreading code and the second inverse spreading code such that no influence is given to the second spreading code and the second inverse spreading code. Otherwise, the first spreading codes and the first inverse spreading codes may have a spreading gain such that no influence is given to the second spreading code and the second inverse spreading code.